1. Field of the Invention
The present invention relates to an encoding and modulating method for wireless communication apparatus that transmits or receives data through a wireless propagation channel, and a decoding method for the wireless communication apparatus.
2. Description of the Related Art
For years, a commitment to a subject of how to realize efficient communications while attaining the Shannon limit, which is the theoretical limit of information through a channel, by appropriately combining an encoding technique and a modulation technique as a wireless communication technique for mobile communications or the like has been made in earnest. Therefore, a specialized encoding (error-correction encoding) technique has been adopted. According to the IS-95 based on the code division multiple access (CDMA) technique that was introduced in the mid 1990s, a convolutional code that specifies a constraint length of 9 (k=9) and a Viterbi decoding system are used in combination to achieve communications under a low signal-to-noise ratio. Eventually, as already known, a system capacity has been markedly increased. In the third-generation mobile telecommunications system IMT-200 and its innovated systems of the high-speed packet access (HSPA) system and the evolution data-only (EvDO) system, turbo coding and iterative decoding are adopted as the error-correction encoding technique. Further, for new-generation systems, adoption of the low density parity check (LDPC) code has been discussed. In the innovated systems of IMT-2000, a multi-valued modulation technique has been adopted in order to achieve high-speed data communications. 8 phase shift keying (PSK), 16 quadrature amplitude modulation (QAM), and 64 QAM are stipulated as multi-valued modulating techniques, and the numbers of bits that can be transmitted in the form of a symbol according to the respective techniques are 3, 4, and 6 respectively. For demodulating multiple bits, gray mapping is adopted as a bit allocation (mapping) method in order to draw out a larger amount of information. The gray mapping is widely adopted because of the feature that since bits are allocated (mapped) so that adjoining signal points (symbols) will be different from each other in only one bit, an amount of information a sole demodulator (demapper) can draw out is maximized.
The foregoing approach can be said to pursue specialized modulating processing, which is paired with modulation, independently of specialized decoding processing that is paired with encoding. In contrast, a technology called bit interleaved coded modulation with iterative decoding (BICM-ID) (“Bit-interleaved coded modulation with iterative decoding” by X. Li and J. A. Ritcey (IEEE Communications Letters, vol. 1, pp. 169-171, 1997) has been introduced and has attracted attention. The BICM-ID technology is such that demodulating processing paired with modulation and decoding processing paired with encoding are iteratively executed, and the results of one of the pieces of processing are referenced during the other processing to be performed next time, or in other words, a so-called turbo signal processing technique is implemented together with the demodulating processing and decoding processing. According to the BICM-ID technology, as described in “Optimized Symbol Mappings for Bit-Interleaved Coded Modulation with Iterative Decoding” by F. Schereckenbach, N. Gortz, J. Hagenauer, and G. Bauch (IEEE GLOBECOM 2003, pp. 3316-3320, 2003), the specialties in an encoding technique and a modulating technique are not improved separately but are matched each other in order to realize excellent specialty.
According to “Optimized Symbol Mappings for Bit-Interleaved Coded Modulation with Iterative Decoding” by F. Schereckenbach, N. Gortz, J. Hagenauer, and G. Bauch (IEEE GLOBECOM 2003, pp. 3316-3320, 2003), when a BICM-ID technique is constructed by adopting as an encoding technique the convolutional code which specifies a constraint length of 3 (K=3) and an encoding ratio of 1/2 (R=1/2), and adopting a mapping technique called modified set partitioning (MSP) (FIG. 30) that is a modulation technique inferior to the gray mapping in terms of specialty, the BICM-ID technique exerts more excellent specialty than a BICM-ID technique adopting the gray mapping. According to “Extended Mappings for Bit-Interleaved Coded Modulation” by P. Henkel (IEEE PIMRC, 2006), a BICM-ID technique is constructed by adopting as an encoding technique a convolutional code which specifies a constraint length of 2 (K=2) and an encoding ratio of 1/2 (R=1/2), and adopting as a modulation technique special mapping which is called extended mapping and in which a larger number of bits than the number of bits capable of being originally mapped is allocated as shown in FIG. 32, the BICM-ID technique exhibits excellent specialty. In “Optimized Symbol Mappings for Bit-Interleaved Coded Modulation with Iterative Decoding” by F. Schereckenbach, N. Gortz, J. Hagenauer, and G. Bauch (IEEE GLOBECOM 2003, pp. 3316-3320, 2003) and “Extended Mappings for Bit-Interleaved Coded Modulation” by P. Henkel (IEEE PIMRC, 2006), the BICM-ID techniques are described to exhibit excellent specialty by employing extrinsic information transfer (EXIT) analysis introduced in “Convergence Behavior of Iteratively Decoded Parallel Concatenated Codes” by S. ten Brink, (IEEE Transactions on Communications, Vol. 49, No. 10, pp. 1727-1737, October 2001).
In contrast, a BICM-ID technique employing a code, which exhibits excellent specialty by itself, such as the aforesaid LDPC code is described in “Design of Low-Density Parity-Check Codes for Modulation and Detection” by S. ten Brink, G. Kramer, and A. Ashikhmin (IEEE Transactions on Communications, Vol. 52, No. 4, April 2004).